Optimisation of DRC ICP-MS for determining selenium in plants

Abstract

An inductively coupled plasma spectrometer (ICP-MS) equipped with a dynamic reaction cell (DRC) was used for determining Se in plant samples. A study was made of the ways of removing polyatomic interferences that affect the determination of the most abundant isotopes of selenium, using CH4 or, alternatively, NH3 as a reaction gas. We optimized the efficiency of the bandpass tuning and the cell gas flow rate for suppressing potentially interfering product ions formed by ion–molecule reactions in the dynamic reaction cell of an inductively coupled plasma mass spectrometer. 115In+ was selected as an internal standard for determining Se by DRC ICP-MS. We monitored the rate of reaction between 115In+ and CH4 or NH3, and the product ions created from reactions between In+ and CH4 or NH3. The trueness of the analytical results was assessed by the use of CRMs for Se in plants. The Se experimental results obtained by DRC ICP-MS and by conventional ICP-MS methods were compared with certified values. The values obtained by DRC ICP-MS at m/z 78 with NH3 as the reaction gas were in good agreement with all analysed reference materials at an RPq value of 0.75, zero RPa and cell gas flow rate 0.8 mL min−1. The use of ammonia instead of methane was more appropriate for determining Se in plant samples. Higher reaction efficiency was achieved for suppressing the interferences of double charge ions of lanthanides, and, in addition, determining 80Se+ with CH4 as the reaction gas in plant material with a higher Br content, than in the certified reference material NIST Tomato Leaves 1573a (1300 ng g−1Br), which suffers from strong interference from 1H79Br+.